1. Field of the Invention--the present invention relates to the field of purifying water and, more particularly, to systems and methods utilizing biomass such as aquatic plants in an impoundment for purifying impurities in water.
2. Statement of the Problem--A need exists for a dense biomass system for controlling impurities in water impoundments such as ammonia, nitrogen, phosphorous, and heavy metals. The benefits of using a biomass to purify water are well known. For example, as ammonia is converted into nitrogen in a body of water, often dissolved oxygen levels are depleted resulting in the death of fish and aquatic plants. When nitrogen and/or phosphorous are present in water, algae blooms can occur because the nitrogen and phosphorous are a primary food source for various undesirable algae species. Heavy metals within a water body often make it unsafe for drinking. Biomass management systems are used for managing aquatic plants in water impoundments such as ponds, lakes, runoff basins, etc. The type and quantity of plants are designed and controlled in an impoundment to consistently absorb nitrogen, phosphorous and heavy metals. The aquatic plants also provide a net increase in the dissolved oxygen level if managed properly. If aquatic plants are left unmanaged, they will "take over" a body of water and the plants may begin to die and then compound the problems with respect to impurities in the water.
In one prior art approach, as represented by U.S. Pat. Nos. 4,888,912 and 5,106,504, phytocompatible containers are utilized to enclose non-rooted "submersed" aquatic plants below the surface of the water in the photic zone of the impoundment. The "submersed" aquatic plants extract nutrients and trace metals from the water. The phytocompatible containers are used in conjunction with rooted "submersed" vegetation that extracts nutrients and trace metals. Such phytocompatible containers are designed to remain out of sight and submerged below the surface of the water. In this submersed design separate regions in the impoundment are required, one elevated plateau region (7 feet deep) for the rooted submersed plants and a second deeper perimeter trench (8-20 feet deep) for the submerged non-rooted plants. The perimeter trench also attracts colder water which tends to sink and to displace the warmer water to the center plateau surface where it enhances plant growth. The submerged containers are designed to fully contain the non-rooted submerged plants including the propagating portions. The harvest of the submerged rooted and non-rooted of plants occur periodically. With the harvesting the impurities collected by the plants are removed in the harvested plants. The plateau region can be harvested with harvest machines. The containers must be lifted out of the water and opened for harvesting.
U.S. Pat. No. 4,536,988 to Hogen sets forth an aquatic biomass containment barrier. The '988 patent sets forth a floating containment barrier grid structure for containing floating aquatic plants in a body of water. The floating structure is anchored by cables and stakes to the impoundment. The '988 patent is designed to grow floating aquatic plants only. In the preferred embodiment, duckweed is grown to remove unwanted nutrients from the water. The duckweed is periodically harvested. The '988 structure is designed to enable the large scale growing of duckweed as a cash crop and is designed to slightly submerge when a harvester or barge harvests the duckweed. Thin plastic sheets are used to construct the grid structure and to contain the duckweed in individual interconnected square barrier segments. Each barrier segment has a wave barrier so as to prevent the duckweed from one segment from blowing or riding a wave into the next segment.
U.S. Pat. No. 5,010,837 to Hirose sets forth a floating marine paddy farm which provides a floating raceway that secures the ocean water from the fresh water in a buoyant support. On the surface of the fresh water hydroponic paddy rice plants can be grown.
The article by Gotaas, et al., Photosynthetic Reclamation of Organic Waste, The Scientific Monthly, pp. 368-372 (Dec. 1954) discusses the advantages of using biomass material to purify water. This article also discusses the advantages of orienting the tanks in the North-South direction in order for the tanks to receive direct sunlight throughout the day.
In U.S. Pat. No. 4,333,263 "Algal Turf Scrubber", it is recognized that wave action can increase biomass productivity. The '263 patent sets forth an algal scrubber which includes a wave generating mechanism.
A need exists for a dense biomass management system which utilizes both floating non-rooted plants and bottom dwelling rooted plants in the same region of the impoundment to maximize the density of the biomass and so that the different types of plants can be designed and managed to control the particular impurities in the water. The addition of floating plants over the bottom dwelling plants must occur without causing the bottom growing plants to be excessively shaded (and, therefore, not thriving) and to enable both types of plants to be easily harvested. Finally, the system should permit wave action to occur on the floating plants to increase productivity.
3. Solution to the Problem--The present invention sets forth a biomass management system that allows rooted bottom dwelling plants to grow and remain healthy on the bottom of a water impoundment while allowing rootless floating plants to grow and remain healthy above them.
The present invention allows the non-rooted, floating plants to be contained in a large surface area provided by elongated channels where they would naturally occur and thrive. The unique elongated channels of the present invention allow the water to pass through the net of the channel and further allows waves on the surface to agitate the floating plants to increase productivity and to circulate the surface water within the channel, thereby preventing a stagnate surface area from developing. Furthermore, the system allows the sunlight to reach the bottom dwelling plants while containing the floating plants so that they cannot take over the surface. The elongated channels of the present invention can be linked together as needed to provide the correct amount of rootless, floating aquatic plants with the correct amount of bottom dwelling plants to properly manage the nutrient loading of the water impoundment.
The system of the present invention is designed to work in harmony with the daytime path of the sun, if required, to maximize the amount of sunlight penetrating under the floating channels to the bottom dwelling plants from morning to evening. The floating channels of the present invention are designed to keep the rootless, floating aquatic plants at the surface in their natural habitat for optimum growth characteristics and for ease of access for maintenance.
Finally, harvesting of the bottom dwelling plants can occur in a conventional manner while the floating plants in the channels can be harvested from alongside or above the channels.